Retinal degeneration in rhesus monkeys, Macaca mulatta. Survey of three seminatural free-breeding colonies

Abstract

The ophthalmoscopic investigation of 162 seminatural, free-breeding rhesus monkeys is reported. The age (ranging from 1 month to 21 years), the maternal lineage and sibling relationships of these monkeys were known. Age-related changes in the fundus appearance, macula, retinal vessels, remnants of the hyaloid arteriole and choroidal patterns are described. Two major fundus pathologies were observed: a macular pigmentary anomaly and paramacular drusen-like lesions. These appeared separately or in combination, unior bilaterally. Less frequent pigmentary anomalies were observed outside the macula. The macular pigmentary anomalies and drusen-like lesions affect both sexes (male: 44%; female: 56%). Both pathologies were observed in fairly severe form in very young animals (1 to 3 years), but the frequency increases with age. In the old adult group (16–21 years) one or both eyes of 83% of the animals were affected. Since the same pathology with a some-what lower frequency was also found in a genetically unrelated group of (12+-year-old) monkeys living in cages in a completely different environment, and in a genetically-related group living on a different diet, environmental and nutritional causes in etiology were excluded. The hereditary nature of the disease is highly probable, but the mode of inheritance could not be determined from the data available. The fundus pathology described resembles in many respects some human hereditary retinal degenerations, and therefore it is hoped that further studies of this disease will shed some light on the etiology and pathophysiology of pigmentary and drusen-like disorders in humans.